Atomizing apparatus having a liquid accumulation cavity



Dec 21, 1965 G. BURNSIDE ETAL 3,224,680

ATOMIZING APPARATUS HAVING A LIQUID ACCUMULATION CAVITY Filed June 11,1964 2 sheets-sheet 1 EEE] Il t (nel GILBERT L. BURNSIDE JOHN W. MISTELEINVENTORS ATTORNEYS l- VALVE RESERVOIR N48 DeC- 21, 1965 G. L. BURNSIDEETAL 3,224,630

ATOMIZING APPARATUS HAVING A LIQUID ACCUMULATION CAVITY Filed June 1l,1964 2 Sheets-Sheet 2 FIG. 2

PowER 2/ SOURCE V20 GILBERT L. BURNSIDE JOHN W. MISTELE INVENTORSATTORNEYS United States Patent ii" 3,224,680 Patented Dec. 21, 1965 ICC3,224,680 A'I'MIZING APPARATUS HAVING A LIQUID ACCUMULATIN CAVITYGilbert L. Burnside, Oak Park, and .lohn W. Misteie, Detroit, Mich.,assignors to Ford Motor Company, Dearborn, Mich., a corporation ofDelaware Filed June 11, 1964, Ser. No. 375,425 9 Claims. (Cl. 239-223)This application is a continuation-impart of copending applicationSerial No. 116,814, led on lune 13, 1961, and now abandoned.

This invention relates to a method and apparatus for comminuting liquidcoating materials and for the electrostatic transportation of thecomminuted particles for deposition on an article. It is particularlydirected to the repetitions electrostatic painting of similar articlesin which the paint is first atomized by centrifugal force and then,after receiving an electrical charge, transported to and deposited onthe surface of an article to be painted.

The painting art has resorted to the use of rotating atomizing headssuch as metallic cups or discs for the production of a charged mist orspray of paint. These metallic atomizing heads are rotated about theirown axis, and paint is fed to the central portion of the head fromwhence it flows to the periphery of the head under the influence ofcentrifugal force. At the periphery, the paint may also be atomizedelectrostatically and, therefore, departs from the atomizing head in adirection which amounts to the vector sum of the centrifugal andelectrostatic forces.

Present practices of delivering liquid coating materials such as paintto the center portion of an atomizing head require a conduit meansextending through the inner shaft which supports the head as illustratedin U.S. Patent 2,759,763. Another type of atomizing head in the priorart is center fed through a nonrotating nozzle located in the center ofa cup which is connected to a paint supply tube as depicted in U.S.Patent 2,922,584.

The method for center feeding paints to the atomizing surfaces or edgesof atomizing devices used for electrostatic painting in the presentstate of the art has been found to be unsatisfactory as it is difficultto obtain uniform wetting of the atomizing surfaces or edge, especiallyat high speeds of rotation, Incomplete or uneven wetting results inspitting or nonuniform atomization of the paint. Also, liquid coatingmaterials and cleaning solvents have a tendency to penetrate thebearings supporting the rotating atomizing head through the inherentclearances between rotating and nonrotating members. Seepage of coatingmaterials such as red oxide primer, which is highly abrasive, results inextensive Wear of bearing surfaces. Further, low viscosity solvents usedfor flushing liquid coating materials from the atomizing devicespenetrate the bearings and seals due to the vibrations and centrifugalforces present in the operation of these atomozing devices. Seals suchas O rings and gaskets are chemically attacked by the solvents that alsodissoli? and destroy the effectiveness of lubricants applied to movingparts.

The method and apparatus of this invention overcome the deficiency ofthe center feed atomizing devices by feeding the liquid coating materialfirst to a cavity machined into the hub portion of the atomizing headwhere complete distribution of the coating material is effected. Thenthe coating material flows uniformly from the cavity through a pluralityof passages to the feeding zone of the atomizing head from whence itcontinues to be distributed to the periphery of the head so as to wetthe entire edge under the influence of the centrifugal and inertialforces. Actually, the cavity acts as a storage reservoir for the liquidcoating material before it is forced out through the passages at auniform rate and pressure to the feeding Zone.

An object of this invention is to provide an atomizing device to be usedfor the commercial application of electrostatic paint coatings involvingcentrifugal atomization.

A further object of this invention is to provide an atomizing device inwhich the liquid coating material is fed from a cavity located in onesurface of the atomizing head through passages to the periphery of thehead where it is atomized.

A still further object is to provide a spraying device for electrosaticcoating which is relatively free from breakdown and requires little orno maintenance.

Other objects and advantages of this apparatus will become more apparentas this description proceeds, particularly when considered inconjunction with the drawings in which:

FIGURE 1 is a side elevational View, partially in section, of thespraying apparatus of this invention; and,

FIGURE 2 is a front view of the atomizing head of the spraying apparatusof this invention.

In FIGURE 1 can be seen a spraying device 11 comprising an atomizinghead 12 which may be in the form of a bell, cup, disc, or plate. Theatomizing head 12, in this instance, has a tubular hub portion 13 on oneend which is integrally formed with a cup-shaped body portion 14 on theother end. The cup-shaped body portion 14 is concentric and coaxial withthe tubular hub portion 13.

The atomizing head 12 is rotated by a driving means, such as an airmotor 15, which is supplied by compressed air through coupling 16. Spentair is exhausted from the air motor 15 through a second coupling 17. Theair motor 15 is contained in a housing 18 by screws 19. The housing 18,the air motor 15, and its associated atomizing head 12, which arepreferably constructed out of metal, are charged to a high potential bya voltage source 20 by means of conduit 21.

The housing 18 is attached to a support plate 22 by studs 23. Each stud23 is locked to a handle 24 by a dowel pin 25. Manual rotation of thehandle 24 adjusts the housing 1S and its contained spraying device 11 toassure that the atomizing head 12 is properly aligned with the surfacesof an article (not shown) to be coated. The support plate 22 is attachedto a clamp 26 which permits the mounting of the spraying device 11 on apost 27. The post 27, which is usually manufactured from a dielectricmaterial, may be installed in a spray booth or other enclosure.

The atomizing head 12 is provided with a bore 28 which is concentricwith the axis of rotation of the atomizing head 12 and the air motor 15.A bushing 29 in the bore 28 receives shaft 30 of the air motor 15. Theatomizing head 12 is driven by the shaft 30 through a pin 31 held in adrive plate 32. The drive plate 32 is secured to the atomizing head 12by screws 33. To retain the atomizing head 12 on the shaft 30, a stopplate 34 is screwed onto the threaded end portion of the shaft 30. A setscrew 35 locks the stop plate 34 to the drive plate 32 in order toretain the rotating atomizing head 12 on the shaft 35i during theoperation of the spraying device 11.

The hub portion 13 of the atomizing head 12 has a concentric annularcavity 36 machined into its back surface 37. The internal peripheral andbottom surfaces of the cavity 36 are sloped to form a recessedcontinuous outer corner 38 at their junction. A continuous radius 39 isformed in the corner 38. The cup-shaped body portion 14 of the atomizinghead 12 has an internal, concave-shaped feeding Zone 40 terminating in acircular atomizing edge 41.

A plurality of passages 42 place the corner 38 of the cavity 36 incommunication with the feeding zone 40 of the body portion 14 of theatomizing head 12. The passages 42 are sloped outwardly from therecessed outer corner 38 of the cavity 36. The cavity 36, as it isannular shaped, also has a continuous recessed inner corner 54.

An axially mounted liquid coating material delivery tube 43 is held inthe housing 18 by a screw 44. The delivery tube 43 is supplied with aliquid coating material through a hose 45 connected to a coupling 46. Avalve 47 installed in the hose 45 regulates the flow of the liquidcoating material that may be fed from a reservoir 48 by a pump or by anyother suitable means. A nozzle 49, which is attached to the front end ofthe delivery tube 43, feeds the liquid coating material to the innercorner 54 of the cavity 36 of the atomizing head 12.

As seen in FIGURE 2, the nozzle 49 is angled in order to feed the liquidcoating material to the corner 54 of the cavity 36 in a counterclockwisedirection. This is the same angular direction in which the atomizinghead 12 is rotated (as designated by arrow). The passages 42, as bestseen in FIGURE 2, are equally spaced to permit the uniform distributionof the liquid coating material from the feed tube 43 to the feeding zone40 of the atomizing head 12. Experimentally, it has been determinedthat, for liquid coating materials such as automotive paints, theangular spacing of the passages 42 should not exceed 6.

In the utilization of this apparatus for priming of sheet metal parts,eighty tubular passages, each of .062 inch diameter and placed l1/2apart, were found to be satisfactory.

In the application of the method and apparatus of this invention, liquidcoating materials are fed to the cavity 36 while the atomizing head 12is being rotated by the air motor 15. It is essential that the atomizinghead 12 rotates rapidly to enable the paint to be atomized bycentrifugal action. Rotating speeds of 1,200 to 5,00() r.p.m have beenfound very satisfactory for a six-inch atomizing head 12 with aconventional liquid prime coating material. The rotational speed may bevaried to accommodate such variables as paint viscosity, paintcomposition, and temperature. The high potential impressed on theatomizing head 12 and the steep electrostatic gradient immediatelyadjacent to the edge 41 of the atomizing head 12 charge the atomizedparticles of paint and permit their acceleration, transportation, anddeposition by the electrostatic field existing between the atomizinghead 12 and the article to be painted.

The liquid coating material flows from the reservoir 48 to fill thecavity 36 of the atomizing device 11 when valve 47 is opened. Then thecoating material is forced outwardly from the cavity 36 through thepassages 42 at a uniform rate and pressure to the feeding zone 40 byvirtue of the centrifugal and inertial forces acting on it. The liquidcoating material continues to flow to the peripheral edge 41, wettingthe entire feeding zone 40 of the atomizing head 12 during its rotation.No liquids come into contact with the shaft 30 lor the bushin-g 29 tocause seepage between the rotating and stationary members of theatomizing device 11.

It has been found that the provision for a large number of tubularpassages 42 results in a more uniform distribution of liquid coatingmaterial on the entire surface of the feeding zone. This avoids what iscommonly referred to as a striping effect or incomplete wetting of thesurface of the cup. To assure that the flow of liquid coating materialis effected through all passages at one time and at a uniform rate andpressure, it is essential that the liquid coating material has to beaccumulated within the cavity to a certain depth prior to beingdistributed therefrom to the feeding zone. This is achieved by feedingthe coating material to the inner corner 54 and by sizing the tubularpassages 42 so that they initially impede the ow, thereby causing abackup of liquid coat- Cil ing material in the cavity 36 to establish areservoir therein. The steady accumulation of liquid coating material inthe cavity 36 will provide a sufficient pressure head due to thecentrifugal and inertial forces acting thereon to force the liquidcoating material through the passages 42 at a uniform pressure and rateto the feeding zone 40 to establish a flow balance between the nozzle 49and the peripheral edge 41 at the speed of rotation of the atomizinghead 12. The angling of the nozzle 49 further assures uniformdistribution of the liquid coating material in the cavity 36, especiallyat high speeds of rotation.

The design of the atomizing device 11 of this invention permits theutilization of more than one delivery tube 43 to feed paint to theliquid receiving cavity 36 of the atomizing head 12. As can be seen inFIGURE l, a second delivery tube 50 with its nozzle 51 (as shown inphantom lines), may be mounted around the periphery of the atomizinghead 12. This second feed tube 50 may be connected to a second reservoir52 and regulated by a valve 53 installed between the reservoir 52 andthe atomizing device 11. Delivery tube 50 and other delivery tubes, ifdesired, may be installed in housing 18 similar to delivery tube 43.

The use of plurality of delivery tubes 43 and 50 permits the mixing ofliquid coating materials of different colors or compositions by openingvalves 47 and 53 simultaneously. Also, it is possible to switch from onecolor to a second color without requiring the flushing out of thevarious delivery tubes 43 and 50. An alternate arrangement can beeffected to permit the instantaneous cleaning of the atomizing head 12by connecting delivery tube 50 to the reservoir 52 filled with asolvent. Then, by opening valve 53, the atomizing head 12 is cleanedwhile paint may be retained in delivery tube 43, ready for painting, bykeeping valve 47 closed.

We claim:

1. An apparatus for atomizing liquids comprising a rotatable atomizinghead, driving means for rotatably supporting said atomizing head, saidatomizing head comprising a cupshaped body portion on one end integrallyformed with a hub portion at the other end, said cupshaped body portionhaving a concave feeding zone terminating in a continuous peripheraledge, an annular recessed liquid receiving cavity located in said hubportion, said liquid receiving cavity having a continuous recessed innercorner and a continuous recessed outer corner connected by a bottomsurface, at least one conduit means extending .into said cavity forintroducing liquids to be atomized at the recessed inner corner of saidliquid receiving cavity, and a plurality of passages leading from saidrecessed outer corner of said cavity to said feeding zone, each of saidpassages being of a size that causes said liquids to be accumulated insaid cavity before being forced through said passages at a uniformpressure and rate to said entire feeding zone under the influence ofcentrifugal and inertial forces.

2. An apparatus for atomizing liquids comprising a rotatable atomizinghead, means for rotatably supporting and driving said atomizing head inone direction, said atomizing head comprising a cup-shaped body portionon one end integrally formed with a hub portion at the oth-er end, saidcup-shaped body portion having a concave feeding zone terminating in acontinuous peripheral edge, and. an annular recessed receiving cavitylocated in said huby portion, said annular recessed receiving cavityhaving a continuous recessed inner corner and a continuous recessedouter corner connected by a bottom surface sloped outwardly and towardsaid one end of said atomizing head, a nozzle extending into said Cavityfor introducing liquids to be atomized to said atomizing head at thecontinuous recessed inner corner, said nozzle being angled in the samedirection in which said atomizing head is rotated, and a plurality oftubular passages leading from said recessed outer corner to said feedingzone, each of said passages being of a size that causes said liquids tobe accumulated in said cavity before being forced through said passagesat a uniform pressure and rate to said entire feeding zone under theinfluence of centrifugal and inertial forces.

3. An apparatus for atomizing liquids comprising a rotatable atomizinghead, driving means for rotatably supporting said atomizing head, saidatomizing head cornprising a cup-shaped body portion on one endintegrally formed With a hub portion on the other end, said cupshapedbody portion having a concave feeding zone terminating in a continuousperipheral edge, an annular recessed liquid receiving cavity located insaid hub portion, said cavity having a continuous recessed inner cornerand a continuous recessed outer corner connected by a bottom surface, atleast one conduit means extending into said cavity for introducingliquids to be atomized at the recessed inner corner of said liquidreceiving cavity, and a plurality of tubular passages leading from saidrecessed outer corner of said cavity to said feeding zone, each of saidpassages being of a size that causes said liquids to be accumulated insaid cavity before being forced through said passages at a uniformpressure and rate to said entire feeding zone under the influence ofcentrifugal and inertial forces.

4. An apparatus for atomizing liquids comprising a rotatable atomizinghead, driving means for rotatably supporting said atomizing head, anannular recessed liquid receiving cavity located on one side of saidrotatable atomizing head, a liquid feeding zone located on the otherside of said rotatable atomizing head, said liquid receiving cavityhaving a recessed inner corner and a recessed outer cornerconcentrically disposed with respect to said atomizing head, a pluralityof nozzles angularly spaced from each other for introducing a pluralityof liquids to be atomized at the recessed inner corner of said liquidreceiving cavity, and means for selectively introducing liquids to beatomized into the liquid receiving cavity from said nozzles, and aplurality of passages leading from said recessed outer corner to saidliquid feeding zone, each of said passages being of a size that causessaid liquids to be accumulated in said cavity before being forcedthrough said passages at a uniform pressure and rate to said entirefeeding zone under the influence of centrifugal and inertial forces.

S. An apparatus for atomizing liquids comprising a rotatable atomizinghead, driving means foi rotatably supporting and driving said atomizinghead in one direction, said atomizing head comprising a cup-shaped bodyportion on one end integrally formed with a hub portion on the other endlying on the same axis of rotation, said cupshaped body portion having aconcave feeding zone terminating in a continuous peripheral edge, anannular re cessed liquid receiving cavity located in said hub portion,said annular liquid receiving cavity having a continuous recessed innercorner and a continuous recessed outer corner concentrically disposedwith respect to the axis of rotation, said recessed inner corner andsaid recessed outer corner being connected by a bottom surface, theconcave feeding zone of said cup-shaped body portion axially spacedoutwardly from the bottom surface of said liquid receiving cavity, atleast one conduit means extending into said cavity for introducingliquids to be atomized at the recessed inner corner of said liquidreceiving cavity, and a plurality of diagonally extending tubularpassages leading from the recessed outer corner of said liquid receivingcavity to said concave feeding zone, each of said passages being of asize that causes said liquids to be accumulated in said cavity beforebeing forced through said passages at a uniform pressure and rate tosaid entire feeding zone under the influence of centrifugal and inertialforces.

6. The apparatus as described in claim 5 and which is furthercharacterized in that said tubular passages are uniformly angularlyspaced not more than 6 apart.

7. The apparatus as described in claim 5 and which is furthercharacterized in that said bottom surface of said cavity is slopedoutwardly and forwardly towards the peripheral edge of said cupshapedbody portion of the atomizing head.

8. The apparatus as described in claim 5 and which is furthercharacterized in that said nozzle is angled in the same direction inwhich said atomizing head is rotated.

9. A self-cleaning apparatus for atomizing liquid coating materialscomprising a rotatable atomizing head, a shaft, means for rotating saidshaft, a cup-shaped body portion on one end integrally formed with thehub portion on the other end lying on the same axis of rotation, saidcup-shaped body portion having a concave feeding zone terminating in acontinuous peripheral edge, an annular liquid receiving cavity in saidhub portion defining a hub lying on the axis of rotation, said liquidreceiving cavity being axially spaced from and positioned from the endopposite from said concave feeding zone, said liquid receiving cavityhaving a continuous recessed inner corner and a continuous recessedouter corner, an end portion of said shaft being non-rotatably receivedin said hub, at least one conduit means extending into said cavity forintroducing liquids to be atomized at the recessed inner corner of saidcavity, said atomizing head being rotated at a speed suicient to causesaid liquid coating material to flow from said recessed inner corner tosaid recessed outer `corner and through said tubular passages to theperipheral edge of said atomizing head and to be atomized from saidperipheral edge under the influence of centrifugal action, a secondconduit means for introducing a liquid cleaning agent at the recessedinner corner of said liquid receiving cavity angularly spaced from saidfirst conduit means, said atomizing head being rotated at a speedsufficient to cause said liquid cleaning agent to flow from saidrecessed inner corner to said recessed outer corner and from therethrough said tubular passages to said peripheral edge to clean thesurface of said atomizing head previously in contact with said liquidcoating material, and means for selectively introducing liquid cleaningagent and liquid coating material into said liquid receiving cavitythrough said first and said second conduit means, respectively, and aplurality of tubular passages placing said outer corner in communicationwith said concave feeding zone, each of said passages being of a sizethat causes said liquids to be accumulated in said cavity before beingforced through said passages at a uniform pressure and rate to saidentire feeding zone under the influence of centrifugal and inertialforces.

References Cited by the Examiner UNITED STATES PATENTS 2,287,067 6/1942Schmidt 239-7 2,374,462 4/ 1945 Schmidt 239-7 2,814,527 1l/1957 Peebleset al 239-214 2,83 6,464 5/1958 Dickinson 239-214 2,917,241 12/1959Waldrum 239-214 2,975,756 3/1961 Reindl et al 239-15 3,043,521 7/1962Wampler 239-214 3,082,956 3/1963 Point 239-15 3,121,024 '2/ 1964 Wampleret al. 239-223 3,133,702 5/1964 Stelchek 239-214 3,144,209 8/1964Griiliths 239-223 FOREIGN PATENTS 647,264 7/ 1928 France. 1,110,35010/1955 France.

703,441 3/ 1941 Germany.

770,530 3/1957 Great Britain.

M. HENSON WOOD, IR., Primary Examiner.

EVERETT W. KIRBY, Examiner.

1. AN APPARATUS FOR ATOMIZING LIQUIDS COMPRISING A ROTATABLE ATOMIZING HEAD, DRIVING MEANS FOR ROTATABLY SUPPORTING SAID ATOMIZING HEAD, SAID ATOMIZING HEAD CONPRISING A CUP-SHAPED BODY PORTION ON ONE END INTEGRALLY FORMED WITH A HUB PORTION AT THE OTHER END, SAID CUPSHAPED BODY PORTION HAVING A CONCAVE FEEDING ZONE TERMINATING IN A CONTINUOUS PERIPHERAL EDGE, AN ANNULAR RECESSED LIQUID RECEIVING CAVITY LOCATED IN SAID HUB PORTION, SAID LIQUID RECEIVING CAVITY HAVING A CONTINUOUS RECESSED INNER CORNER AND A CONTINUOUS RECESSED OUTER CORNER CONNECTED BY A BOTTOM SURFACE, AT LEAST ONE CONDUIT MEANS EXTENDING INTO SAID CAVITY FOR INTRODUCING LIQUIDS TO BE ATOMIZED AT THE RECESSED INNER CORNER OF SAID LIQUID RECEIVING CAVITY, AND A PLURALITY OF PASSAGE LEADING FROM SAID RECESSED OUTER CORNER OF SAID CAVITY TO SAID FEEDING ZONE, EACH OF SAID PASSAGE BEING OF A SIZE THAT CAUSES SAID LIQUID TO BE ACCUMULATED IN SAID CAVITY BEFORE BEING FORCED THROUGH SAID PASSAGES AT A UNIFORM PRESSURE AND RATE TO SAID ENTIRE FEEDING ZONE UNDER THE INFLUENCE OF CENTRIFUGAL AND INERTIAL FORCES. 